1. Field of the Invention
The present invention relates to an image display device using an electronic photographic method, and more particularly to an image display device for displaying an image formation of an information processing system such as a computer as a visual image.
2. Description of the Prior Art
An electronic photographic method and an image display device disclosed in Japanese Patent Application Laid-Open No. 98746/1983 and Japanese Patent Application No. 151278/1982 proposed by the assignee of the present invention are explained with reference to FIG. 1.
FIG. 1 is a side elevational view of an image display device. An endless photoconductor belt 8 which serves as an image carrier and is guided by guide rolls 9, 10, 11 and 12 and intermittently driven by drive means (not shown) is arranged in a case 1, an output light from a semiconductor laser (not shown) modulated by an image electrical signal is scanned unidirectionally by a scanner 5, and a back side of the photoconductor belt 8 is illuminated by the output light through an f-.theta. lens 6 and a mirror 7. The photoconductor 8 may comprise a photoconductive layer formed on a transparent and conductive base.
A developing unit 15 having a sleeve 17 including a magnet 16 rotated in a direction of an arrow is arranged to face the surface of the photoconductor belt 8 at an exposure position A, and a conductive and magnetic developing agent 18 supplied onto the surface of the sleeve is uniformly restricted by a blade 19 and contacts the surface of the photoconductor. A D.C. voltage is applied between the sleeve of the developing unit and the substrate of the photoconductor by a D.C. power supply (not shown), and rollers 13 and 14 are arranged rear behind the exposure and developing position so that the photoconductor belt 8 is kept flat to more precisely keep the distance between the photoconductor surface and the developer sleeve. The toner image formed on the photoconductor belt by the beam irradiation at the position A facing the developing unit 15 is fed to a display station 2.
The display station 2 comprises a square window opening 3 in a front side of the case 1 and a glass or synthesized resin transparent member 4 which covers the window opening 3 so that the toner image on the photoconductor can be directly viewed externally. When the predetermined visual image area aligns with the position of the window opening 3, the photoconductor 8 is stopped for a selected time period automatically or by switch operation. The toner image on the photoconductor surface is viewed through the transparent member 4 and the window opening 3.
A lamp 20 is provided as required to erase previously developed images from the photoconductor. It is lit only during the movement of the photoconductor belt and turned off when it is stopped.
When the display content is to be changed, the photoconductor 8 is moved and the photoconductor having the toner image thereon can be used again as it is. Accordingly, a cleaner for erasing the toner image is not necessary.
The principle of the image formation applied to the above image display device is disclosed in Japanese Patent Application Laid-Open No. 98746/1983 and Japanese Patent Application No. 151278/1982. A brief explanation is given here with reference to FIGS. 2 and 3.
FIG. 2 shows charges in a light area of an information light. As the tner 18 having a voltage applied thereto through the sleeve 17 contacts to the photoconductor, an electric field is applied to a photoconductive layer 8c. If the information light is irradiated, photo-carriers e are created in the photoconductive layer 8c and they are guided to the vicinity of the surface of the photoconductive layer 8c under the action of the electric field. As a result, a strong elastrostatic force of attraction acts between the toner 18 conveyed on the sleeve by the magnetic force of the rotating magnet 16 and the photoconductive layer 8c so that the toner 18 is deposited to the photoconductive layer 8c on the surface of the photoconductor 8. The sleeve 17 may be rotated instead of the magnet.
In the illustrated example, the photoconductive layer 8c is an N-type semiconductor and a positive voltage is applied to the toner 18. Therefore, the carriers e created in the vicinity of the substrate in the photoconductive layer 8c by the illumination of the information light L are guided toward the surface of the photoconductive layer 8c. As a result, the strong electrostatic force of attraction acts between the toner 18 and the photoconductor 8 and the toner 18 is deposited on the photoconductor.
FIG. 3 shows charges in a dark area. Because of the electric field applied between the toner 18 and the transparent conductive layer 8b of the substrate, an electrostatic force of attraction acts therebetween. However, the force is weak because the photoconductive layer 8c is present therebetween and they are distant from each other. Accordingly, the toner 18 is removed from the photoconductive layer or the surface of the photoconductor 8 by the magnetic force of the rotating magnet 16 arranged in the sleeve 17 and the deposition force among the particles of the toner 18.
When the tner image on the photoconductor 8 is to be changed, a new image can be formed by moving the image area past the exposure position. If a toner bearing area of the photoconductor is to be changed to a non-bearing area, the toner 18 having the electrostatic force of attraction reduced is removed by the magnetic field of the magnet 16 and a light area having no toner deposited thereon is formed. On the other hand, when the toner is to be maintained, the carriers e are again injected by the information light and the toner 18 is carried against the magnetic field so that the toner is maintained. Accordingly, the toner image on the photoconductor surface does not affect the next image formation and no separate cleaning means is necessary.
In FIGS. 2 and 3, numeral 8a denotes a polyethylene terephthalate film which supports the transparent and conductive layer 8b, and E denotes a power supply for applying a voltage to the sleeve. The photoconductive layer may be a CdS layer or ZnO, Se, SeTe or AS.sub.3 Se.sub.2 layer used in the prior art electro-photographic process.
In the image display device of this type, the image carrier such as the photoconductor belt on which the images are formed is repeatedly used as the belt is rotated, and the image carrier 8 is repeatedly bent and deformed. This more or less affects the durability of the image carrier 8. The image carrier 8 which is repeatedly stressed will be subject to cracks, defects, breaks or tears and finally lose the function of carrying an image. In addition, because of the belt structure, a deskew mechanism is required. Thus, the device is complicated. Contamination by the scattering of toner as the photoconductor rotates also raises a problem.
In the image display device of this type, a total updating of the displayed image is attained but a partial updating of the displayed image is not attained.